Recently, a liquid crystal display device has tended to become large-sized, and perfection and a thin-layer type are required in a color filter to be employed in the device.
Furthermore, good optical clarity and patterns with high resolution are also required. Still further, there is required the decrease of costs for the preparation of the color filter.
For that reason, there inevitably requires an improvement of yield and productivity.
A color filter is composed of a transparent substrate such as a glass plate on which there are coated layers having pixel elements containing essential three primary colors and optional black color by triangular array, mosaic array, and stripe array, particularly, pixel elements for a charge connection device (CCD) require patterns with high resolution, for example, from submicrons to tens of microns.
Furthermore, pixel elements for a liquid crystal display device (LCD) require patterns with high resolution, for example, from tens of microns to two hundreds microns or so, and the pixel elements require systematical arrays according to the fixed order of each of every colors in the essential three primary colors and optional black color.
Heretofore, color filters have been prepared by repeating a process in which there is coated a photo-setting colored filter composition onto a transparent substrate such as a glass plate, and then the layer formed by coating is developed by exposing to photo-energy after drying, and further removing unexposed portions by organic solvents or aqueous alkali solutions in order to fix patterns.
It is to be noted that the photo-setting colored filter composition includes coloring materials such as pigments or dyes, a photo-curable resin which is a medium for dispersing the coloring materials, additionally polymerizable monomers and/or oligomers and, optionally, dispersants for the pigments. At the present time, aqueous alkali solutions are mainly employed in dissolving from a viewpoint of environmental protection.
As the photo-curable resin, acrylic-based resins have been employed because of excellent weatherability and minor change in colors. For example, Japanese Patent Unexamined Publication (Kokai) No. 53201/1993 (corresponding to U.S. Pat. No. 5,232,634) discloses a photo-setting colored filter composition comprising a (meth)acrylic resin, multi-functional acrylates such as trimethylolpropane triacrylate, pigments, dispersants, and photo-initiators. However, although the photo-setting colored filter composition is excellent in weatherability, there are insufficient properties such as alkali resistance in a coated layer, solvent resistance, and moisture resistance after curing because the acrylic resin itself which is a medium for dispersing the pigments cannot be cured.
Furthermore, Japanese Patent Unexamined Publication (Kokai) No. 230212/1994 discloses a photo-setting colored filter composition comprising photo-curable resins in which double bonds are introduced into acrylic resins having hydroxyl groups through a diisocyanate compound, pigments, and photo-initiators.
The photo-setting colored filter composition can provide cured layers having an excellent alkali resistance and solvent resistance owing to capability of curing in the acrylic resin itself which is a binder.
However, as the photo-setting colored filter composition containing the acrylic resins exhibits tackiness even after removal of solvents, there has been a problem that a photographic mask often becomes dirty during exposing to photo-energy.
In the case when there is decreased the amount of monomers or oligomers for diluting mixed in order to decrease tackiness, photo-curability and resolution cannot be sufficiently obtained.
On the other hand, a solder resist composition does not contain coloring materials compared to the photo-setting colored filter composition. It is usually employed for preparing a permanently protecting layer onto a printed circuit board. In the circuit board, the solder resist composition is coated onto all residual portions except portions to be soldered in electrically-conductive portions in order to prevent oxidation and corrosion of the circuit together with preventing unpreferred blot by solder.
As a process for protecting a printed circuit board by a layer formed from a solder resist composition, there is known a process in which a thermosetting type resist ink is printed by a screen printing method, and then the printed resist ink is thermally cured or cured by an ultraviolet ray. However, during being printed, the resist ink printed by a screen printing method causes bleeding, blotting, and flowing, resulting in that it is not appropriate for coatings onto a recent large-scale integrated circuit board.
In order to solve the problems, a photographic process was thought out in which layer formed from a solder resist composition is exposed to light through a photographic film having a fixed pattern, and then the layer is developed with a developer to form a desired pattern.
The solder resist composition employed in the photographic process, that is, a photographic solder resist composition includes a dry-film type and liquid-type photographic solder composition. Layer formed from the dry-film type composition readily causes foams, and it includes anxiety in thermal stability and anti-strippability and expensive costs.
Accordingly, the liquid-type photographic solder resist composition is primarily employed at the present time.
It is to be noted that organic solvents have been conventionally employed as a developer in the process using the liquid-type photographic solder resist composition. However, from a viewpoint of environmental protection, there is thought out a process in which a diluted aqueous alkali solution is employed as a developer. As a photographic solder resist composition developed by a diluted aqueous alkali solution, JP-61243869-A discloses a liquid type solder resist composition which comprises a compound obtained by an addition reaction of a polybasic anhydride with a reaction compound between a novolak type epoxy compound and an unsaturated monocarboxylic acid. The liquid type solder resist composition is excellent in thermal stability.
However, it exhibits tackiness even in the completion of predrying in order to remove solvents. Predrying at higher temperatures partially causes curing of the composition, unpreferably resulting in that developability becomes worse after exposed to light. Furthermore, the novolak type epoxy compound can not be readily modified, unpreferably resulting in that various demands of properties for a resist composition are not satisfied.
Furthermore, JP-01139619-A discloses a photographic solder resist composition which comprises a compound obtained by an addition reaction of glycidyl(meth)acrylate with an acrylic resin having a high acid value. Although the compound is excellent also in predrying properties because main chains in the acrylic structure can be freely modified, it is insufficient in basic properties such as curability and developability as a photographic solder resist composition.
Still further, it is difficult to control the reaction between carboxylic group and epoxy group, unpreferably resulting in increasing viscosity or readily causing gelation.
In addition, JP-01289820-A discloses a curable resin composition mixing a compound obtained by an addition reaction of a (meth)acrylate having an alicyclic epoxy group in place of glycidyl(meth)acrylate with an acrylic resin having a high acid value. However, in the case when the curable composition is employed as a solder resist developed by an alkali, it is exceedingly poor in developability by an alkali because of insufficient solubility in an alkali. Furthermore, in the curable composition, there is a problem that there is caused separation of components when being stored because of poor solubility in monomers or oligomers for diluting and with inorganic fillers.
In order to solve the disadvantages in the prior arts, as a result of extensive investigations, the present inventors have now completed the present invention.